1. Field of the Invention
The present invention relates to an active vibration insulator, especially, an active vibration insulator for actively inhibiting the vibrations of vibration generating sources, such as vehicle engines, from transmitting.
2. Description of the Related Art
Conventionally, an active vibration insulator has been equipped with an electromagnetic actuator for generating active vibrating forces, such as solenoid, for example. When the electromagnetic actuator is under an inoperative malfunction because of plunger lock or broken wire, for instance, there arises a problem, such as the flow of over current in the electromagnetic actuator.
Hence, Japanese Unexamined Patent Publication (KOKAI) No. 8-270,723, for example, discloses to detect the malfunction of the electromagnetic actuator. According to the patent publication, the electromagnetic actuator is judged to be under a malfunction when the maximum value of residual vibrations, which are detected by an acceleration sensor, exceeds a threshold value, and when the intervals of the maximum-value generation show the same cyclicity as those of the vibrating signals of an engine.
However, in the malfunction judgement set forth in Japanese Unexamined Patent Publication (KOKAI) No. 8-270,723, it is extremely difficult to determine the threshold value, which are compared with the maximum value of residual vibrations. This results from the fact that the residual vibrations, which are detected by an acceleration sensor, include various vibration components other than the vibration components resulting from an engine. That is, when the threshold value is low, no malfunction judgment can be made because the maximum value, which does not show the same cyclicity as those of the vibration signals of an engine, has been detected. On the contrary, when the threshold value is high, no reliable malfunction judgment can be made because the maximum value, which shows the same cyclicity as those of the vibration signals of an engine, might not be extracted. On the other hand, it is possible to extract specific-range frequency components from the residual vibrations by a band-pass filter, for instance, in order to carry out the malfunction judgement based on the extracted signal components. However, using a band-pass filter has resulted in highly increasing the manufacturing cost.